Many diagnostic and therapeutic medical devices are equipped to electrically detect physiological events. Such devices may incorporate, for example, intracardiac, subcutaneous, or surface detection components. In some devices, detection of a physiological event is followed by delivery of a therapy or collection of diagnostic data.
In response to detection of a cardiac event, for example, certain medical devices deliver pacing therapy or a high energy antidysrhythmic shock, collect diagnostic data, or both. Some diagnostic and therapeutic electrical medical devices are also equipped to electrically detect respiration. In this case, a device may use detection of respiration as an indication of patient activity level to drive rate-responsive pacing.
To reliably detect physiological events, medical devices generally need to sense very small electrical signals, e.g., on the order of 10 microvolts to 100 millivolts. In addition, the medical device should be capable of discriminating physiological events in the presence of noise. Noise sources may include random device noise, electrode or environment noise, conducted sine wave noise including 50–60 Hz noise, and motion artifact type noise. Noise can make it difficult to reliably detect a physiological event.